1. Field of the Invention
This invention relates to ultrasonic generating systems, and more particularly to such systems which are designed for diagnostic and therapy uses.
2. Brief Description of the Prior Art
Ultrasonic generating systems are in widespread use in the medical field and other fields. In medicine, ultrasonic equipment has many applications, including diagnostic and therapy uses. Conventional ultrasonic generating systems designed for medical applications include an ultrasonic transducer in the form of a piezoelectric crystal mounted in a hand-held applicator and a power supply for supplying a high frequency voltage to the transducer. The crystal is normally in the shape of a disc and mounted on a circular end plate which is pressed against the surface of a patient's skin. The crystal is made to oscillate by the application of the high frequency voltage across the electrodes carried on opposite surfaces of the disc. Each crystal has a resonant frequency, and to optimize the output of the crystal the frequency of the applied voltage is set at the resonant frequency.
The amount of energy transmitted by the crystal transducer is dependent upon the amplitude of the high frequency applied across its electrodes and upon the load applied thereto. The amplitude of the voltage is normally subject to adjustment by the operator. However, the magnitude of the load is dependent upon the degree to which the transducer is coupled to the patient's skin. Where the transducer is separated from the patient's skin by air or a coupling substance with poor ultrasonic transmissiveness, the impedance presented to the crystal will be high and little or no energy will be transmitted to the patient. Water, saline solutions and gels (having good ultrasonic transmissiveness) provide good coupling between the transducer and the patient.
In therapeutic applications, treatment is normally based on the power of voltage applied to the transducer and the application time. An improper coupling of the transducer to the patient's skin during treatment reduces the amount of ultrasonic energy actually transmitted to the patient, thereby providing less than the prescribed treatment for a given application time.
In addition to the need to ensure that the prescribed amount of ultrasonic energy is transmitted to the patient, there is a need to ensure that the oscillator frequency is maintained at the resonant frequency of the transducer crystal. In prior art ultrasonic generating systems the oscillator for driving the crystal is tuned by the manufacturer after the entire system is assembled. Crystal replacement or aging of the electronic components in the power supply frequently requires that the oscillator be returned, a task normally performed by the manufacturer at the factory. Shipment of the system back to the manufacturer for such retuning is time consuming, expensive and removes the equipment from the operative status.
The present invention overcomes the above problems.